1) Those are fine. 2) It depends on context. Nick's answer is right if you are talking about someone keeping a secret. It's also an expression used about something unpopular. It implies that not only would no one pay money for the unpopular thing, it is so awful that no one will take it even if it's free. For example: "No one wants to buy those green, orange, and electric blue skirts. They are very ugly." "You couldn't even give them away if you tried." 3) "I'll just get $10 worth of gas." is fine in the US. 4) Try "I am, but it isn't that bad."

Q1: Those questions are just fine and that's what we'd say. Q2: I'd need more context but we give something away when we don't want something like old clothes maybe or it could be some kind of offer/promotion where things are being offered to people for free Q3: "I'm just going to put in....." We can use "get" i.e. "I need to get some gas" but we wouldn't really use it if we're already at the gas station. Q4: "Are you terrified of heights?" But your suggested answers don't really make sense to me.

1) The examples you gave are perfectly fine. You can definitely use 'have' in that way . 2) The literal meaning is what it says, and it can be used this way. But it is often used as an expression meaning 'Couldn't tell on them'. Meaning: 'couldn't report their (secret) actions (or something about them) to a third party'. 3) You would generally use 'get', at least where I come from. However, either way, the "just" goes before the verb and you do not use an apostrophe in the plural form of nouns. So the sentence would be: "I will just get 10 dollars worth of gas." Apostrophes are used to show posession. Eg: the dollar's value = the value of the dollar. 4) In this case, the more correct vesrion of your first example would be the one that use 'get'. To correct form of your second example would be 'I am, but it doesn't go that far.'